Unitary absorbent multilayered core

ABSTRACT

The present invention is directed to a unitary absorbent core including a first fibrous absorbent layer of (a) natural fibers, synthetic fibers or a mixture thereof, (b) a binder which is a synthetic binder fiber or powder, a hydrophilic emulsion polymer binder or a mixture thereof, the fibrous absorbent layer having an upper surface and a lower surface, the lower surface in contact, optionally coextensively in contact, with an upper surface of a synthetic carrier which has a lower surface integral with a first hydrophobic vapor-transmissive moisture barrier. The present invention is also directed to a receptacle for food incorporating the unitary absorbent core. The present invention is also directed to a filter element incorporating the unitary absorbent core.

This application claims the benefit of U.S. Provisional Application Ser.No. 60/345,049, filed Nov. 9, 2001, which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention is directed to an absorbent core for use withpackaging and displaying poultry, fish, meat, and other foods which tendto exude fluids after packaging. More particularly, the invention isdirected to an absorbent core including an absorbent stratum or strataintegral with a moisture barrier.

BACKGROUND OF THE INVENTION

Conventionally, foods such as fresh poultry, fish, meat, and other foodswhich tend to exude fluids after packaging, are packaged forrefrigerated display by employing a tray to receive the food. Generally,a transparent or translucent plastic film is wrapped and sealed aroundthe food placed on the tray itself and the tray to provide a finished,sealed package. The tray provides structural integrity and acts as areservoir for fluids. Ideally, the tray also serves as a moisturebarrier.

One type of tray is generally constructed from compressed wood pulp.However, the structural integrity of this type of tray is diminished bythe absorption of fluids from the product placed on the tray. Anothertype of tray is made from a non-absorbent material which can retain itsstructural integrity upon exposure to fluids and moisture. Suitablenon-absorbent materials include thermoplastic materials, such aspolyethylene, polypropylene, polystyrene, and polyvinyl chloride.Although trays made from thermoplastic materials as described above haveseveral advantages in terms of cost, weight, aesthetics, durability, andother characteristics, the inability of these materials to absorbmoisture often results in the accumulation of fluid exuded from the foodproduct placed on the tray. The tray with the food product iscustomarily wrapped and optionally heat sealed with a transparent,flexible thermoplastic film so that the finished product may bedisplayed in a refrigerated display case in such a manner that theconsumer may view the food product directly through the packaging.Accordingly, the accumulation of fluids in the tray surrounding the foodproduct is undesirable because it results in an unsightly, unappetizingand therefore unappealing packaged product. Furthermore, and moreimportantly, although the package is sealed with a flexible transparentfilm the accumulated fluid may leak from the package. In addition,accumulated fluids may promote the growth of bacteria.

One approach to solving this problem has been to provide an absorbentpad between the upper surface of the non-absorbent tray and the foodproduct. In theory, the pad will absorb the exuded fluids from the foodproduct preventing the accumulation of free fluids within the package.Another proposed solution to the problem has been to provide a separatereservoir within the tray such that fluids exuded by the food productare drained away from contact with the product, generally by providing aretaining surface above the bottom wall of the tray. The retainingsurface includes drain holes extending therethrough such that fluiddrains from the product retaining surface and is retained above thelower wall of the tray. Examples of food trays and pads for usetherewith are shown in U.S. Pat. Nos. 3,575,287, 4,275,811, 4,321,997,4,410,578, 4,865,855, 4,929,480, 4,949,897 and WO 99/32286. Thedisclosure of each of the foregoing U.S. patents is hereby incorporatedby reference.

The use of prior absorbent pads for the absorption of fluids from apackaged food product suffers from several disadvantages. Typically,after the pad is saturated with fluid it tends to stick to the foodproduct and must be physically separated from the food product by theconsumer after the package is opened. Because the pad is saturated withfluids exuded by the food product, this is a generally unappealingexercise.

The use of a separate fluid reservoir to separate and retain exudedfluids, suffers from other disadvantages. The construction of the foodtray is complex, requiring at least two layers separated by a free spaceto serve as the reservoir. Further, it is difficult to keep the fluidwithin the reservoir when the package is upset from a level orientation.Thus, it is an object of the present invention to provide an absorbentcore for use with food packaging and which is capable of absorbing allor substantially all of the fluid which may be exuded from a foodproduct placed within the tray during its shelf life. It is anotherobject of the present invention to provide an absorbent core which maybe used in a food package to maintain an aesthetically pleasing andsanitary package. It is yet another object of the present invention toprovide an absorbent core which upon absorbing fluid from the foodproduct prevents or at least minimizes rewet, or fluid contact betweenthe fluid and the food product.

SUMMARY OF THE INVENTION

The present invention is directed to a unitary absorbent core includinga first fibrous absorbent layer of (a) natural fibers, synthetic fibersor a mixture thereof, (b) a binder which is a synthetic binder fiber orpowder, a hydrophilic emulsion polymer binder or a mixture thereof, thefibrous absorbent layer having an upper surface and a lower surface, thelower surface in contact, optionally coextensively in contact, with anupper surface of a synthetic carrier which has a lower surface integralwith a first hydrophobic vapor-transmissive moisture barrier. Thepresent invention is also directed to a receptacle for foodincorporating the unitary absorbent core. The present invention is alsodirected to a filter element incorporating the unitary absorbent core.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph depicting hydrostatic head versus meltblown content ofSMS carriers.

FIG. 2 is a cross-sectional view of one embodiment of an absorbent core(8) of the present invention. The absorbent core (8) of the presentinvention includes a fibrous, absorbent layer (10) having an upper fluidreceiving surface and a lower surface, and a vapor-transmissive moisturebarrier integral with the lower surface of the absorbent layer: a secondfibrous absorbent layer (12); and a third absorbent layer (14).

FIG. 3 is a cross-sectional view of a food tray (16) including anabsorbent core (8) of the present invention. The absorbent core (8)rests upon the upper surface (15) of the tray (16). The absorbent core(8) of the present invention includes a fibrous, absorbent layer (10)having an upper fluid receiving surface and a lower surface, and avapor-transmissive moisture barrier integral with the lower surface ofthe absorbent layer; a second fibrous absorbent layer (12); and a thirdabsorbent layer (14).

FIG. 4 is a cross-sectional view of another embodiment of the presentinvention. The absorbent core (18) is a multi-strata structure with 4absorbent layers (14, 12, 10, 20). Superabsorbent polymers (SAP) (22) isincorporated into one of the absorbent layers (10).

FIG. 5 is a cross-sectional view of another embodiment of the presentinvention. The absorbent core (8) is a multi-strata structure with 3absorbent layers having pores useful for filtration (24).

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to an absorbent core which may be usedwith food packaging to absorb and retain fluid exuded by a food product,while minimizing rewet of the food product by the fluid absorbed by thecore. With reference to FIG. 3, food tray 8 may be made from anysuitable thermoplastic material such as polyethylene, polypropylene,polystyrene, or polyvinyl chloride cellular materials. The tray ispreferably made from polystyrene foam obtained from either expandedpolystyrene or sheet molding.

Absorbent core 8 rests upon the upper surface 15 of tray 16. Core 8 maybe constructed from a variety of materials as set forth in detail below.

The outer surfaces of absorbent core 8 may optionally be compatible withlayer 15 such that the core and the layer may be laminated. If desired,the lamination surface of either layer 15 or core 8 may be treated toenhance lamination, by for example flame treatment or corona dischargetreatment. In this embodiment, core 8 is laminated to all or a portionof the surface of layer 15. Alternatively, core 8 may be cut to desiredsize and simply placed within tray 16 such that the food product willrest upon the core. Optionally, the cut-out core 8 may be glued orotherwise adhered to the upper surface of layer 15 to hold the core inplace within the tray. Acceptable adhesives may be any adhesivecompatible with the two layers, and acceptable for use in a foodpackaging environment. Examples of such adhesives include ethylene vinylacetate (EVA); acrylics, urethanes, polyamides, polyesters, polyamides,etc. An example of a suitable EVA adhesive is Airflex 460, availablefrom Air Products. All U.S. patents cited herein are hereby incorporatedby reference. In the case of a conflict in terminology, the presentdisclosure controls.

The unitary absorbent core of the present invention includes a fibrous,absorbent layer having an upper fluid receiving surface and a lowersurface, and a vapor-transmissive moisture barrier integral with thelower surface of the absorbent layer. Many of the materials useful inthe practice of this invention are described in U.S. Patent ApplicationPublication No. 2002-0013560-A1, which is hereby incorporated byreference in its entirety.

The fibrous absorbent core may be formed using materials and techniqueswell known in the art. For example, the core may include one or morelayers or strata of natural or synthetic fibers, hereinafter referred toas an “absorbent layer.” Cellulosic fibers are preferred for use in theabsorbent layer. The absorbent layer may be formed using wetlaid orairlaid techniques, although airlaid processes are preferred. Binders,such as, for example, wet strength agents, latex emulsions,thermoplastic bicomponent fibers (“bico”), thermoplastic bondingpowders, including polefins and polyesters, and combinations thereof,may be incorporated into the absorbent layer. The term “multibonded” isused to describe an absorbent layer incorporating a combination ofbinders including a preferred combination of latex and bico. Smallamounts of a water-based hydrophilic emulsion binder may be applied tothe surfaces of the absorbent layer to reduce “dust-off” of loose fibersand other particles. Further, for improved absorption of fluids,superabsorbent polymers (SAP) may be incorporated into the absorbentlayer. SAP may be incorporated into the absorbent layer as particles,granules, flakes, fibers (SAF), etc., and may be included as a discretestratum or mixed with the fibers of .the absorbent layer. Materials suchas fillers, perfumes, surfactants, and additives may be included in thecore. Desirable absorbent cores suitable for use in the practice of thisinvention and components suitable for use in the cores are described inWO 99/16961, WO 99/63922, WO 99/63923, WO 99/63925, WO 00/41882, WO00/38607, all of which are hereby incorporated by reference.

In a preferred embodiment, the unitary absorbent core of this inventioncan be described as a multi-zone or multi-strata or multilayer absorbentstructure, which has two or more distinct strata. As used herein, theterms “stratum” and “strata” refer to the layered regions which make upthe unitary structure. The unitary structure is constructed byassembling the strata in a continuous manner in a series of unitoperations which results in the production of the unitary absorbentcore. The strata of the unitary structure is not an assembly or laminateof preformed layers or plies which are assembled on a converting line.Notwithstanding the previous statement, in an optional variation of apreferred embodiment related to the continuous airlaid process of thisinvention, a carrier tissue or a synthetic carrier of low basis weightor a separate stratum may be used to facilitate the production of afibrous absorbent layer having a plurality of strata. In one embodiment,a preferred unitary absorbent core of this invention has two or morestrata, at least one of which is a fibrous absorbent layer having anupper fluid receiving surface and a lower surface, and avapor-transmissive moisture barrier integral with the lower surface ofthe absorbent layer. In a preferred embodiment, the unitary absorbentcore is produced in a continuous manner using airlaid technology, wherean individual forming head provides material for a single stratum andconstitutes one unit operation in the series. Other unit operations inthe series include application of a froth, foam, dry powder, or spraywhich produces the vapor-transmissive or nontransmissive moisturebarrier, and may include compression and calendering and dryingoperations. The moisture barrier may be applied at any stage of themanufacture of the unitary absorbent core, e.g. after all the stratahave been formed, or after any one or more strata have been formed.

Generally herein, the term “froth” is used to describe foam that is oflow viscosity and of poor stability, which is easily collapsible afterapplication to the lower surface of the fibrous absorbent layer to forma hydrophobic vapor-transmissive moisture barrier integral with thelower surface of the absorbent layer wherein the moisture barrier has astructure which substantially includes fibers coated with hydrophobicmaterial. The terms “stand-up foam” and “stand-up foam barrier” are usedto describe a more substantial foam, which, after application to thelower surface of a fibrous absorbent layer to form a hydrophobicvapor-transmissive moisture barrier integral with the lower surface ofthe absorbent layer, results in some coating of fibers, but also whereinthe moisture barrier has a reticulated remnant of a barrier materialemulsion extending from the lower surface region of the absorbent layerto form an outer reticulated foam barrier.

The unitary absorbent core of this invention has a basis weight of about75 gsm (grams per square meter) or greater, generally from about 80 toabout 1000 gsm, and preferably from about 100 gsm to about 500 gsm, andmore preferably from about 125 gsm to about 350 gsm.

In another embodiment, a breathable, partially fibrous or nonfibrousnonwoven material or structure including one or more spunbonded,meltblown, conformed, bonded carded, or foamed constituents has a basisweight of about 45 gsm or greater for the entire material or structure.

The unitary absorbent core of this invention has a density of from about0.03 g/cc to about 0.7 g/cc, preferably from about 0.04 g/cc to about0.3 g/cc.

The structures of this invention can include natural fibers, syntheticfibers or mixtures of both natural and synthetic fibers. Examples of thetypes of natural fibers which can be used in the present inventioninclude fluffed cellulose fibers prepared from cotton, softwood and/orhardwood pulps, straw, keaf fibers, cellulose fibers modified bychemical, mechanical and/or thermal treatments, keratin fibers such asfibers obtained from feathers, bagasse, hemp, and flax, as well asman-made staple fibers made with natural polymers such as cellulose,chitin, and keratin. Cellulosic fibers include chemically modifiedcellulose such as chemically stiffened cellulosic fibers by crosslinkingagents, fibers treated with mercerizing agents and cellulose acetate.Examples of suitable synthetic matrix fibers include polyethylene,polypropylene, polyester, including polyester terephthalate (PET),polyamide, polyacetates, cellulose acetate and rayon fibers. Certainhydrophobic synthetic fibers, such as polyolefins, may be surfacetreated with surfactant to improve wettability, or may be useduntreated, depending upon their intended function within the core.

Examples of binders which may be useful in the absorbent structure ofthe present invention include polymeric binders in a solid or liquidform. The term “polymeric binder” refers to any compound capable ofcreating interfiber bonds between matrix fibers to increase theintegrity of the stratum. At the same time, the binder may optionallybind fibers and SAP particles or SAF to each other.

For example, a dispersion of natural or synthetic elastomeric latex maybe used as a binder. Thermoplastic fibers or powder, which are wellknown in the art, are also commonly used to provide bonding upon heatingof the absorbent structure to the melting point of the thermoplasticfiber or powder. Other binders, which can be used for stabilizing theabsorbent structure of the present invention, include bonding agentsused to bond cellulose fibers. These agents include polymers dispersedin water, which are cured after application to the fibrous web andcreate bonds between fibers or between fibers and SAP particles or SAF.Examples of such agents include various cationic starch derivatives andsynthetic cationic polymers containing crosslinkable functional groupssuch as polyamide-polyamine epichlorohydrin adducts, cationic starch,dialdehyde starch and the like. Any combination of the above-describedpolymeric binders may be used for stabilizing the structure of thepresent invention. Binders useful in the structures of the inventioninclude binders in liquid form or having a liquid carrier, includinglatex binders. Useful latex binders include vinyl acetate and acrylicester copolymers, ethylene vinyl acetate copolymers, for example, AirProducts AIRFLEX EP 1188, styrene butadiene carboxylate copolymers, andpolyacrylonitriles, and sold, for example, under the trade names ofAirbond, Airflex and Vinac of Air Products, Inc., Hycar and Geon ofGoodrich Chemical Co., and Fulatex of H. B. Fuller Company.Alternatively, the binder may be a non-latex binder, such asepichlorohydrin and the like.

For bonding the fibers specifically, and for structural integrity of theunitary absorbent core generally, water-based latex binders may be used.Alternatively, or in combination with a latex binder, thermoplasticbinding material (fibers or powders) may be used for bonding uponheating to the melting point of the thermoplastic binding material.Suitable thermoplastic binding material includes thermoplastic fibers,such as bicomponent thermoplastic fibers (“bico”). Preferredthermoplastic binding fibers provide enhanced adhesion for a wide rangeof materials, including synthetic and natural fibers, particles, andsynthetic and natural carrier sheets. An exemplary thermoplastic bicofiber is Celbond Type 255 Bico fiber from KoSa. Other suitablethermoplastic fibers include polypropylenes, polyesters, nylons andother olefins, or modifications thereof. A preferred thermoplastic fiberis FiberVisions type AL-Adhesion-C Bicomponent Fiber, which contains apolypropylene core and an activated copolyolefin sheath.

Functional particles for use in the absorbent cores of the inventioninclude particles, flakes, powders, granules or the like which serve asabsorbents, odor control agents, such as, for example, zeolites orcalcium carbonates, bicarbonates, especially sodium bicarbonate,fragrances, antimicrobial agents and the like. The particles may includeany functional powder or other particle having a particle diameter up to3,000 μ (microns). In some preferred embodiments, the functionalparticles used in the core include super absorbent polymer particles(“SAP”). In one desirable embodiment of this invention, the unitaryabsorbent core contains from about 5 to about 90 percent by weight ofSAP, preferably from about 10 to about 80 percent by weight of SAP, morepreferably from about 10 to about 50 percent by weight of SAP.

U.S. Pat. Nos. 5,147,343; 5,378,528; 5,795,439; 5,807,916; and5,849,211, which describe various superabsorbent polymers and methods ofmanufacture, are hereby incorporated by reference. Examples of the typesof SAP particles which may be used in this invention, includesuperabsorbent polymers in their particulate form such as irregulargranules, spherical particles, staple fibers and other elongatedparticles. The term “superabsorbent polymer” or “SAP” refers to anormally water-soluble polymer, which has been cross-linked. There areknown methods of making water-soluble polymers such as carboxylicpolyelectrolytes to create hydrogel-forming materials, now commonlyreferred to as superabsorbents or SAPs, and it is well known to use suchmaterials to enhance the absorbency of disposable absorbent articles.There are also known methods of crosslinking carboxylatedpolyelectrolytes to obtain superabsorbent polymers. SAP particles usefulin the practice of this invention are commercially available from anumber of manufacturers, including Dow Chemical (Midland, Mich.),Stockhausen (Greensboro, N.C.), and Chemdal (Arlington Heights, Ill.).One conventional granular superabsorbent polymer is based onpoly(acrylic acid) which has been crosslinked during polymerization withany of a number of multi-functional co-monomer crosslinking agents, asis well known in the art. Examples of multifunctional crosslinkingagents are set forth in U.S. Pat. Nos. 2,929,154; 3,224,986; 3,332,909;and 4,076,673, all of which are hereby incorporated by reference. Otherwater-soluble polyelectrolyte polymers are known to be useful for thepreparation of superabsorbents by crosslinking, these polymers includecarboxymethyl starch, carboxymethyl cellulose, chitosan salts, gelatinsalts, etc. They are not, however, commonly used on a commercial scaleto enhance absorbency of disposable absorbent articles, primarily due tolower absorbent efficiency or higher cost.

Superabsorbent particulate polymers are also described in detail in U.S.Pat. Nos. 4,102,340 and Re 32,649, both of which are hereby incorporatedby reference. Suitable SAPs yield high gel volumes or high gel strengthas measured by the shear modulus of the hydrogel. Such preferred SAPscontain relatively low levels of polymeric materials that can beextracted by contact with synthetic urine (so-called “extractables”).SAPs are well known and are commercially available from several sources.One example is a starch graft polyacrylate hydrogel marketed under thename IM1000 (BASF; Portsmouth, Va.). Other commercially available SAPsare marketed under the trademark SANWET (Sanyo Kasei Kogyo; Kabushild,Japan), SUMIKA GEL (Sumitomo Kagaku Kabushiki; Haishi, Japan), FAVOR(Stockhausen; Garyville, La.) and the ASAP series (BASF; Aberdeen,Miss.). Most preferred for use with the present invention arepolyacrylate-based SAPs. As used in the present invention, SAP particlesof any size or shape suitable for use in an absorbent core may beemployed.

The vapor-transmissive moisture barrier integral with the lower surfaceof the absorbent layer is formed by applying a hydrophobic material to afibrous substrate for which it is desirable to impart a barrier to thetransmission of liquids, but for which it is also desirable to permitthe passage of vapors including water vapor. The hydrophobic moisturebarrier comprises a hydrophobic material which at least partially coatsthe fibers of the lower surface of the absorbent layer. The hydrophobicmaterial can be a natural or synthetic polymer, or a mixture thereof.The term “vapor-transmissive moisture barrier integral with the lowersurface of an absorbent layer” as used herein means that the barriermaterial at least partially coats at least some of the individual fibersof the absorbent layer, as shown in FIGS. 5 and 7 of U.S. PatentApplication Publication No. 2002-0013560-A1 (the '560 application), butthat a continuous film is not formed. The absorbent layer remainsvapor-transmissive since the pore structure between the untreatedfibers, shown in FIGS. 4 and 6 of the '560 application, remainssubstantially open after treatment to form the barrier, as shown inFIGS. 5 and 7. With the moisture barrier in place on the substrate, theunitary absorbent core has a hydrohead of 30 mm or greater as measuredby modified EDANA nonwoven repellency test 120.1-80, a strikethrough of1.8 g or less as measured by the standard strikethrough test, an airpermeability of 18 m³/min/m² (60 ft³/min/ft²) or greater as measured bymodified ASTM D 737-96, and a water vapor transmission rate (WVTR) of500 g/m²/24 hr or greater. In one embodiment, the unitary absorbent corehas a hydrohead of 85 mm or greater, a strikethrough of 0.08 or less,and an air porosity of 235 CFM or greater.

In alternative embodiments which employ a synthetic carrier the moisturebarrier may be vapor-nontransmissive or nearly so. In certain of theseembodiments it is desirable to replace the hydrophobic material with ahydrophilic material.

Within the scope of this invention is a vapor-transmissive moisturebarrier integral with the lower surface of an absorbent layer where thehydrophobic barrier material coats at least some of the individualfibers of the absorbent layer, and where a reticulated remnant of abarrier material emulsion extends from the surface region of theabsorbent layer to form an outer reticulated foam barrier as shown inFIGS. 10 and 11 of the '560 application. In FIG. 10, the SEMphotomicrograph at 80× shows several fibers intermingled with thereticulated remnant of the barrier material emulsion.

Hydrophobic materials suitable for use in this invention include a widevariety of materials known for water repellency, such as, for example,water insoluble thermoplastic organic materials including hydrocarbonsand naturally occurring resins from petroleum, asphalt and coal tar,organic silicon compounds including polyorganosiloxanes, polysiloxanescontaining halogens, especially fluorine, halohydrocarbons, especiallypolymers containing chlorine and fluorine, and various polymers in theform of natural or synthetic emulsions. Emulsion polymers suitable foruse in this invention include lattices containing polymers, copolymers,as well as mixtures and blends of polymers and copolymers, containing inpolymerized form one or more monomers of vinyl acetate, vinyl chloride,vinyl alcohol, acrylics, acrylates, acrylonitrile, ethylene, propylene,styrene, butadiene, isoprene, and various halogenated counterpartsthereof.

In a preferred embodiment, the vapor-transmissive moisture barrier isformed by applying a hydrophobic polymeric latex emulsion to the lowersurface of the absorbent layer. In at least one embodiment, it isdesirable that a barrier is produced which has a contact angle for wateron the film cast from an emulsion of about 80° or greater, as measuredby the contact angle test (described below). Suitable hydrophobicpolymeric emulsions include emulsions of both natural and syntheticpolymers, including synthetic latexes. Several manufacturers supply suchlatex emulsions including Rohm and Haas, B. F. Goodrich, Air ProductsPolymers and Unichem Inc. A preferred latex emulsion is Unibond 0930(Unichem Inc., Greenville, S.C.) which is an acrylic polymer. Theemulsion can be applied by a variety of methods known in the art,including spray, brush, doctor blade, roller, and foam. Foam applicationis preferred in this aspect of the invention.

The preferred application process involves the injection of air into anemulsion to form bubbles and create a temporary foam, or froth. In thisapplication process, the collapse of the froth and elimination of airbubbles during the process of drying and curing the emulsion occurs.Advantages of foam application are more uniform reagent distribution,ability to apply reagent at higher solids contents, and more controlover reagent penetration into the substrate.

For the embodiment of this invention where the moisture barrier producedhas a reticulated remnant of a barrier material emulsion extending fromthe lower surface region of the absorbent layer to form an outerreticulated foam barrier, it is preferable to use a foam that hasgreater stability than the easily collapsible foams used for moisturebarrier formation where no outer reticulated foam barrier is produced.For a description of suitable conventional foaming procedures and foamstabilizers and foaming agents, reference is made to Mage, E. W., “LatexFoam Rubber,” John Wiley and Sons, New York (1962) and Rogers, T. H,“Plastic Foams”, Paper, Reg. Tech. Conf., Palisades Sect., Soc. PlasticsEngrs., New York, November, 1964. Most common are the alkali metal,ammonia, and amine soaps of saturated or unsaturated acids having, forexample, from about 12 to about 22 carbon atoms. Examples of suitablesoaps include tallow soaps and coconut oil soaps, preferably thevolatile amine or ammonia soaps, so that the volatile portion isvaporized from the foam. Other useful foaming-foam-stabilizing agentsinclude lauryl sulfate-lauryl alcohol, lauryl sulfate-lauric acid,sodium lauryl sulfate, and other commonly used foamed stabilizers orfoaming agents.

A preferred emulsion for the formation of the moisture barrier producedwith a reticulated remnant of a barrier material emulsion extending fromthe lower surface region of the absorbent layer to form an outerreticulated foam barrier is Unibond 0938 from Unichem, which is anacrylic copolymer dispersed in a water base. Application by foam ispreferred for Unibond 0938.

Unibond 0938 is engineered so that it does not collapse on the surfaceupon which it is foamed. After the Unibond 0938 foam is dried and cured,an elastic, reticulated structure, a reticulated remnant of the barriermaterial emulsion remains on the surface. See FIGS. 8-11 of the '560application, which are scanning electron micrographs (SEMs) of treatedand untreated surfaces.

Generally, whether the moisture barrier formed has a reticulated remnantof the barrier material emulsion is a consequence primarily of thestability of the foam, which is influenced by the nature of the emulsionpolymer in the emulsion, whether a foam stabilizer is used and theprocess conditions during application. In practice this is easilycontrolled.

An alternative method of producing the barrier is the addition of powderto a surface of the material or core, which surface may have beenroatated, and on an airlaid line the powder addtion may be before,after, or through one or more forming heads. After application of thelatex emulsion to the surface of the absorbent layer, the emulsion iscured by removing water by drying or heat application. Optionally,crosslinking agents or other curing agents may be employed. Otheradditives may be included in the emulsion, such as biocides, waterrepellents, fillers and colorants. Whichever application technique isused, it is important that the latex emulsion be applied in a sufficientquantity to at least partially coat a majority of individual fibers inthe surface region of the absorbent layer. As used herein, “surfaceregion” refers to the fibers of the absorbent layer directly exposed tothe surface and several layers of fibers below such outermost fibers toa depth of from about 0.01 mm to about 1.0 mm from the surface, andpreferably from about 0.05 mm to about 0.8 mm from the surface. As usedherein, “partially coat” refers to the average portion of the surfacearea of a specific fiber coated with emulsion. Preferably, the fibersare coated by at least enough emulsion to render the fibers hydrophobic.

At the same time, for some aspects, it is important that the amount oflatex emulsion applied not be so great that a continuous layer or filmof polymer is formed which would block the pores. A continuous layer isdisadvantageous because of the adverse affect on water vaporpermeability of the resultant structure. Alternatively, for applicationswhere water vapor transmission is irrelevant, a nontransmissive barriermay be preferred.

The amount of emulsion necessary to provide coated fibers withoutforming a continuous film or layer depends upon the density of theabsorbent layer, the type of fibers employed, the type and physicalproperties of the emulsion employed, the method of application and themethod of curing the absorbent core.

Without wishing to be bound by theory, it is believed that applicationof at least a partial coating of surface fibers with latex emulsionprovides a hydrophobic moisture barrier, but because a continuous filmor layer is not present, the pores created by adjacent coated fiberspermit transmission of water vapor through the barrier. Fabric waterrepellency and breathability have been studied for several decades (A.W. Adamson, Physical Chemistry of Surfaces, Second Edition, Wiley, 1967,Chapters VII and X). A nonwoven web of fibers can be modeled as a bundleof cylindrical pores (capillaries) of radius r. The fluid pressurerequired to penetrate the interfiber pores of a nonwoven web can beapproximated from Laplace's equation for the penetration of a fluid intoa tube:P=(2O cos O)/r

-   -   where:    -   P=pressure required to push fluid through the tube    -   γ=fluid surface tension    -   θ=advancing contact angle    -   r=pore radius

This equation can be used to describe web wetting (θ<90°, P is positive)or web water repellency (θ>90°, P is negative). In the case of waterrepellency, the fluid will not wet the web unless a pressure of P isapplied to push the fluid into the web. From the equation, barrierquality is predicted to be enhanced by increasing the contact angle witha water-repellent finish. In other words, the pores of the web should berendered as hydrophobic as possible.

Apparent contact angles can be increased by surface roughness on themacroscale and microscale. Application of a waterproofing agent thatcauses microscopic pore surface roughness will lead to an increase inapparent contact angle, thus improving barrier quality.

From the equation, barrier quality is predicted to be enhanced byreducing the size of the interfiber pores. Ideally, the web should be asstrong as possible. As pressure builds, weakness in the web will causedeformation, and deformation increases r, thus lowering pressure P. Webstrength can be enhanced by, for example, increasing the amount ofbinder in the web.

The size of interfiber pores in a fibrous web is determined by the fibersize and the density or extent of compaction of the web. Increasing thedensity of the web can reduce the size of interfiber pores, or usingsmaller diameter fibers at the same density can reduce them. Smallerfibers pack together more efficiently in a densified web, resulting insmaller interfiber pores. From the equation, using smaller fibers servesto decrease r, thus raising pressure P.

Filler material can be added to the hydrophobic emulsion to reduce thesize of interfiber pores. From the equation, the addition of fillerserves to decrease r, thus raising pressure P. The addition of filler tothe treatment of the present invention increases barrier performance bypartially blocking the pores of the nonwoven web, resulting in improvedbarrier quality. Filler suitable for use in the practice of thisinvention include calcium carbonate, bicarbonates, especially sodiumbicarbonate, various kinds of clay (bentonite and kaolin), silica,alumina, barium sulfate, sodium carbonate, talc, magnesium sulfate,titanium dioxide, zeolites, aluminum sulfate, cellulose-type powders,diatomaceous earth, magnesium sulfate, magnesium carbonate, bariumcarbonate, mica, carbon, calcium oxide, magnesium oxide, aluminumhydroxide, pulp powder, wood powder, cellulose derivative, polymerparticles, chitin and chitin derivatives.

From the equation, barrier quality is predicted to be directlyproportional to the fluid surface tension. The barrier treatment shouldbe as durable as possible. Any additives in the barrier treatment thatwill dissolve in the fluid will likely lower its surface tension, thuslowering pressure P.

The contact angle test may be used to determine the contact angle ofwater on films cast from materials used to make the barrier, and inparticular, water-based latex emulsions.

The emulsion is diluted with water to form a solution containing 10%solids. The solution is poured onto a borosilicate microscope slide toform a visible coat. The coated slide is set aside to dry overnight atambient temperature and humidity. The coated slide is cured in aforced-air oven at 140° C. for five minutes. The advancing contact angleis measured using an FTÅ 200 Dynamic Contact Angle and Surface TensionAnalyzer (First Ten Angstroms, Portsmouth, Va.) with reverse-osmosistreated water injected with a 27-gauge needle. The FTÅ 200 measures theadvancing contact angle by the drop shape method.

Contact angles were measured for a naked slide (a “blank”), for Unibond0930 and Unibond 0938 (both acrylic latex emulsions from Unichem Inc.,Greenville, S.C.) and for Airflex 192 (ethylene-vinyl acetate latexemulsion, Air Products Polymers, Allentown, Pa.).

Water prefers to wet some surfaces and prefers to bead on others. Asurface can be classified as hydrophilic, with a water contact angleless than 90°, or hydrophobic, with a water contact angle greater than90°, based on the shape that a drop of water assumes when placed on thatsurface.

TABLE 1 Contact angle measurements for films cast from latex emulsionsMaterial Contact angle Naked glass slide (blank) 47.5 Unibond 0930 95.9Unibond 0938 105.8 Airflex 192 44.4

Table 1 shows results from contact angle measurements for films castwith Unibond 0930 and Unibond 0938 (Unichem Inc., Greenville, S.C.) andAirflex 192 (Air Products Polymers, Allentown, Pa.) latex emulsions.Table B-1 shows that Unibond 0930 and Unibond 0938 were both successfulin rendering the surface of the microscope slide hydrophobic with acontact angle greater than 90°. Table B-1 shows that Airflex 192 was notsuccessful in rendering the slide hydrophobic since it produced acontact angle less than 90°.

Any material capable of delivering a contact angle greater than 90° inthis test would be a candidate for possible use in the presentinvention, provided that the material can be applied to a surface of anabsorbent layer to render it hydrophobic without creating a continuousfilm which does not permit the passage of vapor. The hydrophobicemulsions Unibond 0930 and Unibond 0938 (Unichem Inc., Greenville, S.C.)are preferred latex emulsions for use in the practice of the presentinvention.

In an alternative process for the preparation of a unitary absorbentcore comprising a fibrous absorbent layer having an upper fluidreceiving surface and a lower surface with a hydrophobicvapor-transmissive moisture barrier integral with the lower surface ofthe absorbent layer, a hydrophobic material may be dissolved in asuitable solvent and contacted with the lower surface of the absorbentlayer followed by causing the solvent to be removed. The solution may beapplied to the lower surface of the absorbent layer by spraying, or thelower surface of the absorbent layer may be brought into contact withthe solution by brief partial immersion, followed by draining andevaporation of the solvent.

In alternative embodiments of this invention, the fibrous absorbentlayer of the absorbent core may be replaced wholly or in part bypartially fibrous or nonfibrous structures capable of acceptableperformance in an absorbent core, preferably a unitary absorbent core.Suitable partially fibrous or nonfibrous structures include spunbondwebs, meltblown webs, coform webs, such as meltblown mixed withcellulose fibers, airlaid webs, and bonded carded webs, differentialbasis weight nonwoven webs and high internal phase emulsion (HIPE) andother foam structures.

In other embodiments, the hydrophobic vapor-transmissive moisturebarrier of this invention may be integral with a surface of thermoset orthermoplastic cellular or noncellular material, which may be present ina composite of synthetic or synthetic and natural materials. Varioussythetic nonwoven materials can be used as a carrier in the productionof cores, especially by airlaid processes. The basis weight of thesesynthetic carriers desirably is from about 8 gsm (grams per squaremeter) to about 100 gsm, preferably from about 9 to about 60 gsm, morepreferably from about 13.5 to about 22 gsm. Suitable nonwoven carriermaterials are meltblown, spunbond, carded, needlepunched, garnetted,resin bonded, thermal bonded, and point bonded materials produced from,for example polyethylene, polypropylene, polyesterthphalate (PET), nylon6, nylon 6,6,polylactic acid, polyvinyl alcohol. A preferred group ofcarrier materials contain at least one meltblown element. The presenceof a meltblown element in the carrier in conjuction with the hydrophobicvapor-transmissive moisture barrier integral with carrier is especiallyimportant for realization of superior barrier properties. A preferredcarrier material is a spunbond/meltblown/spunbond nonwoven with a basisweight of from about 10 to about 25 gsm. It is desirable for themeltblown element to be at least about 1 gsm and preferably from about 2gsm to about 12 gsm, more preferably from about 2.5 to about 9 gsm,still more preferably from about 3 to about 7 gsm and still moredesirably from about 4 to about 5 gsm. In other embodiments involvingthe use of synthetic carriers, a second hydrophobic vapor-transmissivemoisture barrier integral with the uppermost fibrous layer may be usedin the absorbent core. The properties of the two moisture barriers, suchas, for example, the basis weight of the hydrophobic material, and eventhe hydrophobicity itself, may be varied so that the core produced hastwo outer surfaces with different properties.

Breathable fibrous materials and unitary absorbent cores of thisinvention desirably have a hydrohead as measured by modified EDANAnonwoven repellency test 120.1-80 of 30 mm or more, preferably of 50 mmor more, more preferably of 70 mm or more, even more preferably of 90 mmor more, still more preferably of 200 mm or more.

Breathable fibrous materials and unitary absorbent cores of thisinvention desirably have a strikethrough as measured by the standardstrikethrough test of 1.8 g or less, preferably of 1.2 g or less, morepreferably of 0.7 g or less, even more preferably of 0.1 or less andstill more preferably of 0.02 g or less.

Breathable fibrous materials and unitary absorbent cores of this aspectof the invention desirably have an air permeability as measured bymodified ASTM D 737-96 of from about 3 to about 7 m³/min/m² (11-22ft³/min/ft²), and for cores to be used for filtration, preferably nogreater than about 10 m³/min/m² (33 ft³/min/ft²). In other embodiments,the air permeability may be very low, approaching zero.

Breathable fibrous materials and unitary absorbent cores of thisinvention desirably have water vapor transmission rate as measured bythe water vapor transmission rate (WVTR) test which is a modification ofASTM E 96-95 of 500 g/m²/24 hr or greater, preferably of 1000 g/m²/24 hror greater, more preferably of 2000 g/m²/24 hr or greater, and even morepreferably of 3000 g/m²/24 hr or greater.

Breathable fibrous materials and unitary absorbent cores of thisinvention having a WVTR of 500 g/m²/24 hr or greater desirably havebarrier effectiveness values of 10 mm or greater, more desirably of 30mm or greater, preferably of 50 mm or greater, more preferably of 75 mmor greater, still more preferably of 100 mm or greater and even morepreferably of 230 mm or greater.

In several embodiments, the breathable fibrous materials and unitaryabsorbent cores of this invention provide structures which are usefulfor food and household applications. Within the scope of this inventionare embodiments where these structures are used in combination with oneor more plastic structural elements know in the art for food storage,transportation, display or presentation, such as, for example, foamtrays for meat, poultry or fish.

In some embodiments, the material or core would be glued, for example,with hot melt adhesive, in a tray. Various configurations are possible,such as, for example, glued in the tray with the barrier facing up,glued in the tray with the barrier facing down, sealed in a pouch, edgesealed or used in various laminates with other layering materials. Apreferred method of use is to simply place a core in a tray with thebarrier facing up.

In several embodiments, the breathable fibrous materials and unitaryabsorbent cores of this invention provide structures which are usefulfor filtration. Within the scope of this aspect of the invention areembodiments where these structures are used in combination with one ormore structural elements know in the filtration art for appropriatecontainment of the breathable fibrous material or unitary absorbent coreso that it may be used in a filtration process.

Test Methods

The following test methods were used to measure water vapor transmissionrate, air permeability, strikethrough and hydrostatic head for thestructures prepared in the following examples.

Water Vapor Transmission Rate

The method is used to determine the water vapor transmission rate (WVTR)through airlaid handsheets and is a modification of ASTM E 96-95.

Apparatus for this test includes a vapometer cup (#68-1, Thwing-AlbertInstrument Co., Philadelphia, Pa.) and a forced-air oven capable ofmaintaining a temperature of 38° C. plus or minus 1° C. (Lindberg/BlueM, Lindberg/Blue M Co., Asheville, N.C., or equivalent). A circularsample 7.6 cm (three inches) in diameter is cut from a handsheet. Onehundred milliliters of deionized water is placed into the vapometer cup.The test material is placed over the cup opening. The screw-on flange istightened over the test material, leaving an exposed sample area of33.17 square centimeters. The initial weight of the cup is recorded. Thecup is placed on a tray and set in the forced-air oven for 24 hours at38° C. After 24 hours, the cup is removed from the oven and reweighed todetermine total water loss. WVTR is calculated as follows:WVTR (g/m ²/24 hours)=[total water loss over 24 hours (g)×301.5]

The report for each test includes the average WVTR (n=3) for treatedsamples compared to the average WVTR (n=3) for the untreated controlmaterial. Note that the relative humidity within the oven is notspecifically controlled in this test.

Air Permeability

This method is a modification of the standard air permeability test forwoven and nonwoven fabrics, ASTM D 737-96. Air permeability through thetreated samples is compared with air permeability through untreatedsamples to give relative permeability effectiveness.

Air permeability of absorbent core handsheets is determined using an airpermeability tester (Model 9025, modified with digital “A” and “B”gauges, U.S. Testing Co., Inc., 1415 Park Ave., Hoboken, N.J. 07030).Specifically, three handsheets per experimental sample (n=3) are testedusing the air permeability tester. For each handsheet, a pressure dropof 1.3 cm (0.5 in.) of water is established across the handsheet.Airflow though the sheet is measured by the pressure drop across anorifice indicated on a vertical manometer. The average manometer readingis converted to air permeability using conversion tables provided by themanufacturer of the air permeability tester. Air permeability isreported as airflow in m³/min/m² and cubic feet per minute per squarefoot (ft³/min/ft²).

Strikethrough

This test is used to measure the resistance of sample materials topenetration by synthetic menses.

Samples are cut into 10.3 cm×10.3 cm (4 in.×4 in.) squares. Each sampleis placed onto a 10.3 cm×10.3 cm (4 in.×4 in.) Plexiglas bottom platewith the treated side facing down. The sample is covered with a 3.2 mm(0.125 in.) thick, 10.3 cm×10.3 cm (4 in.×4 in.) Plexiglas top platewith a 3.2 cm (1.25-in.) diameter hole cut in its center. A 5 ml insultof synthetic menses (room temperature) is introduced through the hole inthe top plate. After waiting for 20 minutes, a tared stack of 10 Whatman#3 filter papers, 110 mm circles, (Whatman International Ltd., England)is placed on the bottom plate beneath the sample. A 2500 g weight isplaced on the Plexiglas top plate and is allowed to stand for 2 minutes.After 2 minutes, the filter papers are removed and weighed.Strikethrough is calculated as follows:Strikethrough (g)=Wet filter paper weight (g)−Tare filter paper weight(g)

This test is usually run in triplicate (n=3) and the average value isreported in the unit of grams.

Hydrostatic Head

Hydrostatic head (hydrohead) is measured by using a modified version ofthe EDANA nonwoven repellency test 120.1-80. This EDANA test is based ontest method ISO 811:1981-EN 20811:1992. The EDANA method is modified byusing a testing diameter of 60 mm; a cylinder length of 100 mm; amanometer diameter of 10 mm (internal); a dosing pump equipped with aT-valve for rapid cylinder filling; and an aqueous test solution of 10%(w/v) calcium chloride (General Chemical Co., Parsippany, N.J.). Thecalcium chloride is used to inhibit swelling of any SAP particles in thetest sample, which might otherwise interfere with web integrity duringthe test. This test is usually run in triplicate (n=3) and the averageresult is reported in the unit of millimeters of hydrohead.

EXAMPLES

The following examples are presented to provide a more detailedunderstanding of the invention. The specific materials and parametersare exemplary and are not intended to limit the scope of the invention.

Layer 1 contains a mixture of fibers and binder, preferably a cellulosicpulp and binder mixture, consisting of some combination of pulp, bondingfiber, optional superabsorbent material and emulsion polymer binder. Thepulp can be any of a number of cellulose fluff pulps. A preferred fluffpulp is FOLEY FLUFFS® from Buckeye Technologies Inc. which was used inthe Examples hereinbelow. The bonding fiber was KoSa F55 bicomponentfiber consisting of a polyester core and a polyethylene sheath. Theemulsion polymer binder was an ethyl vinyl acetate copolymer that sellsunder the trade name AirFlex 192 by Air Products. The superabsorbentmaterial may be in the form of granules, fibers, powder, flakes, withgranules and fibers being preferred. A preferred superabsorbent materialis superabsorbent fiber, Fiberdri™ 1261, from Camelot Technologies,which was used in the Examples hereinbelow. Fiberdri™ has a denier perfilament from about 28 to about 32, a moisture content from about 3 toabout 7 weight percent, a pH of from about 5 to about 7.5. Anotherpreferred superabsorbent material is a superabsorbent fiber, such as,for example, OASIS Type 101 which is cut to a length of 6 mm, has adecitex of 10 and a diameter of from about 25 to about 35 microns. In analternative embodiment, this layer may contain fibers and binder withvery little or no superabsorbent material.

Layer 2 contains a mixture of pulp, optional superabsorbent material andbonding fiber. This mixture of pulp and bonding fiber can be the same ordifferent from the mixture in Layer 1. In this case, the samecomponents, Foley Fluffs®, Fiberdri 1261 and KoSa F55, were used.

In one embodiment where the materials of Layers 1 and 2 are identicaland where these strata are produced in successive unit operations byseparate heads in a continuous airlaid process, the layers merge into asingle stratum with no distinguishable feature to indicate where thematerial laid down by one head ends and the material laid down byanother head begins. Other embodiments of this type may be producedwhere additional layers, which merge into a single stratum, are added tothe structure in additional successive unit operations by separate headsin a continuous airlaid process.

Layer 3 contains a carrier, generally a synthetic carrier, such as, forexample, a spunbond/meltblown/spunbond/ (SMS) polypropylene carrier or aspunbond propylene carrier. A preferred carrier is a 17 gsmspunbond/meltblown/spunbond/ (SMS) polypropylene carrier provided byFirst Quality Nonwovens which was used in the Examples hereinbelow. Thislayer optionally contains an emulsion polymer binder, such as, forexample, a vinyl acetate copolymer such as AirFlex 192 by Air Products.

Layer 4: This layer can consist of various emulsion polymer binders thatare hydrophobic.

Using the above materials, structures were made that require columns ofwater of heights from 86 mm to 245 mm before strikethrough. Thisresistance, called hydrostatic head, is measured using a modifiedversion of test method ISO 811:1981—EN 20811:1992. The reported methodis modified by employing a testing diameter of 60 mm; a cylinder lengthof 100 mm, a manometer diameter of 10 mm (internal), a dosing pumpequipped with a T-valve for rapid cylinder filling, and employing a 10%w/v in water solution of calcium chloride (anhydrous, analytical reagentgrade). The calcium chloride is employed to inhibit swelling of anysuperabsorbent in the test sample, which might otherwise interfere withweb integrity during the test. The tests for food applications weretested with the barrier facing the 10% w/v aqueous calcium chloridesolution.

The materials were also tested for air permeability using a modificationof the standard test for nonwoven fabrics, ASTM 737-96. Air permeabilitythrough treated samples is compared with air permeability throughuntreated samples to give relative permeability effectiveness. The airpermeability for these samples, reported in units of cubic feet perminute per square foot, ranges from 11 to 22.

Experimental

Prior to starting the experimental runs:

The three hammermills in the pilot plant were loaded with Foley Fluffs®.KoSa F55 bicomponent fiber (polyester core/polyethylene sheath) was alsoloaded into two LaRoche towers. Camelot Fiberdri 1261 was loaded intoone LaRoche tower. This LaRoche tower was then set to feed a blend ofthe Camelot Fiber and the KoSa fiber. The blend was 57% Camelot fiberand 43% KoSa fiber. 17 gsm polypropylene SMS by Frist Quality Nonwovenswas loaded onto the unwind stand at the head of the airlaid machine. Thedrying and curing ovens were set to 140° C. AirFlex 192 from AirProducts was diluted with water to 11% solids. Aerosol OT was added toenhance the spray and foam characteristics. If desired, the SMS carriersheet may be perforated.

Preparation of Base Webs:

The SMS carrier sheet was unrolled onto the moving forming wire. As thecarrier sheet traveled through the airlaid machine, a blend of 83.5%Foley Fluffs® from the hammermills and 16.5% Kosa F55 bicomponent fiberfrom the LaRoche tower was fed through one forming head and laid on topof the carrier. The sheet was then sprayed with emulsion binder AirFlex192 on the fluff side. The material was then conveyed through a 30 meterlong through-air oven to dry the binder spray and begin to melt thepolypropylene sheath of the bicomponent fiber. When the material emergedfrom the oven, AirFlex 192 was foamed onto the carrier side of thestructure. The web was then passed through a drum dryer to dry thefoamed emulsion binder and to complete the curing of the binders. Thematerial was then collected in a roll with a minimal amount ofcompaction. For additional samples, the speed of the line was adjusteduntil the correct amount of pulp and bicomponent fiber were beingdeposited onto the moving carrier. Seven samples of varying weights persquare meter (basis weights) were collected in roll form.

On a second day, the SMS carrier sheet was unrolled onto the movingforming wire. As the carrier sheet traveled through the airlaid machine,a blend of 53.5% Foley Fluffs® from the hammermills and 46.5% of abicomponent/superabsorbent blend (42.9 % Kosa F55 bicomponent fiber and57.1% Camelot Fiberdri 1261) from the LaRoche tower was fed through oneforming head and laid on top of the carrier. The sheet was then sprayedwith emulsion binder AirFlex 192 on the fluff side. The material wasthen conveyed through a 30 meter long through-air oven to dry the binderspray and begin to melt the polypropylene sheath of the bicomponentfiber. When the material emerged from the oven, AirFlex 192 was foamedonto the carrier side of the structure. The web was then passed througha drum dryer to dry the foamed emulsion binder and to complete thecuring of the binders. The material was then collected in a roll with aminimal amount of compaction. For additional samples, the speed of theline was adjusted until the correct amount of pulp, superabsorbent fiberand bicomponent fiber were being deposited onto the moving carrier. Fivesamples of varying weights per square meter (basis weights) werecollected in roll form.

Barrier Treatment:

A hydrophobic emulsion barrier was diluted with water to 20% solids. Oneof the twelve rolls of material described above was unrolled and passedthrough the airlaid machine with the carrier facing up. No fibers orpowders were being fed through or between the forming heads of the line.The spray system was used to deliver the hydrophobic emulsion solutiononto the carrier surface in a uniform coating. The material was thenpassed through an oven to dry and cure the hydrophobic emulsion. Thesame procedure and same treatment level was used for two of thematerials containing superabsorbent fiber and for three of the materialswithout superabsorbent fiber.

Testing:

Samples of each of the treated rolls were cut into 4 inch by 4 inchsquares. The squares were then tested for hydrostatic head. Additionalsamples were also cut for Frazier air permeability testing.

For each of the five pads using the 17 gsm carrier from First QualityNonwovens, the hydrohead and Frazier Air Porosity were measured. Example3A and 3D were also tested and shown to have water vapor transmissionrates (WVTR) of >2000 g/m²/24hr.

TABLE 3 Data for Pilot Samples Made with SMS Carrier and HydrophobicBarrier Example Basis Weight, gsm Density, g/cc HH, mm Frazier, cfm 3A302.4 0.067 221 22.1 3B 208.9 0.057 186 11.8 3C 184.2 0.050 141 18.8 3D308.0 0.085 197 16.7 3E 247.6 0.096  95 14.6

Work has been done comparing different carrier sheets, made from olefinpolymers, in combination with a hydrophobic polymer emulsion. There isdistinct difference in barrier effectiveness when the carrier is changedfrom spunbond polypropylene to polypropylene that is formed in layers ofspunbond, meltblown and spunbond (SMS).

Example 1 Comparison of Spunbond Polypropylene to SMS PolypropyleneCarriers

Sample SMS core: The bottom layer of the core consisted of an SMSpolypropylene carrier (17 gsm SMS, First Quality Nonwovens, Inc.,Hazelton, Pa.) on top of which was formed 50 gsm fluff pulp (FoleyFluffs®, Buckeye Technologies, Inc., Memphis, Tenn.), 7 gsm bicomponentbinder fiber (Type AL-Adhesion-C, 1.55 dpf×4 mm, FiberVisions, Macon,Ga.) and 6 gsm of latex adhesive (Airflex 124 ethylene-vinyl acetateemulsion, Air Products Polymers, Allentown, Pa.). The second layerconsisted of 48 gsm fluff pulp (Foley Fluffs®, Buckeye Technologies,Inc., Memphis, Tenn.), 9 gsm bicomponent binder fiber (TypeAL-Adhesion-C, 1.55 dpf×4 mm, FiberVisions, Macon, Ga.) and 3 gsm oflatex adhesive (Airflex 124 ethylene-vinyl acetate emulsion, AirProducts Polymers, Allentown, Pa.) sprayed on top for dust control. Theabsorbent core had an overall basis weight of 140 gsm and a density of0.1 g/cc. Sample Spunbond core: The core consisted of an spunbondpolypropylene carrier (20 gsm hydrophilic spunbond polypropylene, Mogul,Turkey) on top of which was formed 54 gsm fluff pulp (Foley Fluffs®,Buckeye Technologies, Inc., Memphis, Tenn.), 18.9 gsm bicomponent binderfiber (Type 255, 2.8 dpf×4 mm, KoSa, Salisbury, N.C.) and 17.1 gsmsuperabsorbent fiber (Type 101, Oasis, Technical Absorbents, London,UK). The absorbent core had an overall basis weight of 110 gsm and adensity of 0.1 g/cc.

The carrier side of handsheets of each of the two cores were treatedwith varying amounts of hydrophobic barrier (AP12755-95-1, AirProducts,Allentown, Pa.) as shown in the table. The resulting handsheets weretested for hydrostatic head and the results are shown in Table 1.

The data shows that the SMS carrier gives better hydrohead values at allbarrier levels.

TABLE 1 Test Results for Comparison of SMS and Spunbond PolypropyleneCarriers Example 1 Barrier, gsm Hydrohead, mm SMS Core 1 81 5.5 101 9.4132 17 200 Spunbond 2.5 45 Core 5.2 50 11 50 40 50

Example 2 Comparison of Different SMS Carriers

Four pads were made in the lab using different carriers. Pads consistingof 237.8 gsm fluff pulp (Foley Fluffs®, Buckeye Technologies, Inc.,Memphis, Tenn.), 47.1 gsm of bicomponent binder fiber (Type F55, 2.8dpf×6 mm, KoSa, Salisbury, N.C.) and 15.3 gsm of latex adhesive (Airflex192 ethylene-vinyl acetate emulsion, Air Products Polymers, Allentown,Pa.) were formed on top of a carrier. The carriers used werepolypropylene SMS materials as shown in Table 2. After formation, thecarrier side of the pads were treated with 15 gsm of hydrophobic binder(an ethylene-vinyl acetate emulsion from Air Products, Allentown, Pa.).The resulting hydrostatic heads varied widely.

When the hydrostatic head results are graphed versus the availablemeltblown contents of the carriers as in (FIG. 1), there is a linearrelationship shown. The hydrostatic head value is directly related tothe meltblown content of the carrier sheet. Within the family of SMScarriers, the use of carriers with high meltblown content gives the besthydrostatic head values.

TABLE 2 Comparison of SMS Carrier Materials Carrier Meltblown BasisWeight, Hydrohead, Content, Carrier Producer gsm mm gsm Avgol, Holon,Israel 13.5  91 1.50 Avgol, Holon, Israel 17.0 187 3.00 FQN, Hazelton,PA 17.0 267 Not available BBA, Washougal, WA 23.7 291 4.75

Example 3

A pad was made according to the present invention using a 17.0 gsm FQNSMS carrier sheet on which was applied two successive airlaid layers ofa blend of Foley Fluff (55 gsm) and Fibervisions 814ALAD bico fiber (10gsm). A third layer was then applied including a blend of Foley fluff(55 gsm) and Fibervisions 814ALAD bico fiber (9 gsm). The airlaidmaterial was sprayed on the upper airlaid surface with 3.0 gsm ofAirflex 192 and on the exposed surface of the SMS carrier with 11.0 gsmof a proprietary ethylene vinyl acetate copolymer spray as a hydrophobicmoisture barrier. The completed pad had a total basis weight of 225 gsm.After application of the sprays, the material was oven dried and cured.The finished pad had an absorbency of 14 g/g and a hydrohead of 70 mm.

Example 4

A pad was made as in Example 3, except the basis weight of each layerincluded 79 gms of Foley Fluff and 14 gsm of Fibervisions 814ALAD bicofiber. The total basis weight of the pad was 310 gsm. The finished padhad an absorbency of 14 g/g and a hydrohead of 70 mm.

Example 5

A pad was made as in Example 4, except the proprietary EVA spray wassubstituted with an EVA spray from Airflex designated EP1188. The basisweight of the EP1188 was 5.0 gsm. The finished pad had a basis weight of304 gsm. The finished pad had an absorbency of 14 g/g and a hydrohead of70 mm.

Example 6

A pad was made as in Example 3, except the proprietary EVA spray wassubstituted with an EVA spray from Airflex designated EP1188. The basisweight of the EP1188 was 5.0 gsm. The finished pad had a basis weight of219 gsm. The finished pad had an absorbency of 14 g/g and a hydrohead of70 mm.

1. A unitary absorbent core comprising: I) a first fibrous absorbentlayer comprising: a) from about 15 to about 95 percent by weight naturalfibers, synthetic fibers or a mixture thereof, b) from 0 to about 80percent by weight superabsorbent material; and c) from about 5 to about30 percent by weight of a binder which is a synthetic binder fiber orpowder, a hydrophilic emulsion polymer binder or a mixture thereof, and,the fibrous absorbent layer having an upper surface and a lower surface,the lower surface in contact, optionally coextensively in contact, withII) an upper surface of a spunbond-meltblown-spunbond nonwoven syntheticcarrier having a basis weight of from about 9 gsm to about 30 gsm, whichhas a lower surface integral with III) a first vapor-transmissivemoisture barrier, wherein the moisture barrier is hydrophobic orhydrophilic; wherein the unitary absorbent core has a basis weight ofabout 45 gsm or greater and, wherein the unitary absorbent core has anair permeability of from about 3 to about 7 m^(3/)min/m² (11-22ft^(3/)min/ft²).
 2. The unitary absorbent core of claim 1, wherein thecore further comprises in contact, optionally, coextensively in contact,with the upper surface of the first fibrous absorbent layer IV) a secondfibrous absorbent layer comprising a) natural fibers, synthetic fibersor a mixture thereof, and b) a binder which is a synthetic binder fiberor powder, a hydrophilic emulsion polymer binder or a mixture thereof.3. The unitary absorbent core of claim 2, wherein the first, second orfirst and second fibrous absorbent layers further comprisesuperabsorbent material.
 4. The unitary absorbent core of claim 3,wherein the core has an absorbent capacity of from about 10 grams/gramto about 15 grams/gram.
 5. The unitary absorbent core of claim 1,wherein the upper surface of the first or second fibrous layer which isuppermost in the core is integral with a second moisture barrier, whichmay be the same as or different from the first moisture barrier.
 6. Theunitary absorbent core of claim 1, wherein the basis weight of the coreis from about 50 to about 1000 gsm.
 7. The unitary absorbent core ofclaim 6, wherein the basis weight of the core is from about 75 to about350 gsm.
 8. A unitary absorbent core comprising: I) a first fibrousabsorbent layer comprising: a) from about 15 to about 95 percent byweight natural fibers, synthetic fibers or a mixture thereof, b) from 0to about 80 percent by weight superabsorbent material; and c) from about5 to about 30 percent by weight of a binder which is a synthetic binderfiber or powder, a hydrophilic emulsion polymer binder or a mixturethereof, and, the fibrous absorbent layer having an upper surface and alower surface, the lower surface in contact, optionally coextensively incontact, with II) an upper surface of a natural or synthetic carrierwhich has a lower surface integral with III) a firstvapor-nontransmissive moisture barrier, wherein the moisture barrier ishydrophobic or hydrophilic and wherein the unitary absorbent core has abasis weight of about 45 gsm or greater.
 9. The unitary absorbent coreof claim 8, wherein the core further comprises in contact, optionally,coextensively in contact, with the upper surface of the first fibrousabsorbent layer IV) a second fibrous absorbent layer comprising a)natural fibers, synthetic fibers or a mixture thereof, and b) a binderwhich is a synthetic binder fiber or powder, a hydrophilic emulsionpolymer binder or a mixture thereof
 10. A receptacle for containing afood product which tends to exude fluids comprising: (A) a tray forholding a food product; and (B) positioned in the tray, a unitaryabsorbent core having a basis weight of 45 gsm or greater comprising: I)a first fibrous absorbent layer comprising: a) from about 15 to about 95percent by weight natural fibers, synthetic fibers or a mixture thereof,b) from 0 to about 80 percent by weight superabsorbent material; and c)from about 5 to about 30 percent by weight of a binder which is asynthetic binder fiber or powder, a hydrophilic emulsion polymer binderor a mixture thereof, and, the fibrous absorbent layer having an uppersurface and a lower surface, the lower surface in contact, optionallycoextensively in contact, with II) an upper surface of a syntheticcarrier which has a lower surface integral with III) a firstvapor-transmissive or vapor-nontransmissive moisture barrier, whereinthe moisture barrier is hydrophobic or hydrophilic.
 11. The receptacleof claim 10, wherein the first vapor-transmissive orvapor-nontransmissive moisture barrier is vapor-nontransmissive.
 12. Thereceptacle of claim 10, wherein the first vapor-transmissive orvapor-nontransmissive moisture barrier is vapor-transmissive and theunitary absorbent core has an air permeability of from about 3 to about7 m³/min/m² (11-22 ft³/ min/ft²).
 13. The receptacle of claim 10,wherein the synthetic carrier is an SMS nonwoven having a basis weightof from about 9 gsm to about 30 gsm.
 14. The receptacle of claim 10,wherein the core further comprises in contact, optionally, coextensivelyin contact, with the upper surface of the first fibrous absorbent layerIV) a second fibrous absorbent layer comprising a) natural fibers,synthetic fibers or a mixture thereof, and b) a binder which is asynthetic binder fiber or powder, a hydrophilic emulsion polymer binderor a mixture thereof.
 15. The receptacle of claim 10, wherein the first,second or first and second fibrous absorbent layers further comprisesuperabsorbent material.
 16. The receptacle of claim 15, wherein thecore has an absorbent capacity of from about 10 grams/gram to about 15grams/gram.
 17. A filter element comprising: (A) a support matrix, and(B) an absorbent core having a basis weight of 45 gsm or greatercomprising: I) a first fibrous absorbent layer comprising a) naturalfibers, synthetic fibers or a mixture thereof, b) a binder which is asynthetic binder fiber or powder, a hydrophilic emulsion polymer binderor a mixture thereof, the fibrous absorbent layer having an uppersurface and a lower surface, the lower surface in contact, optionallycoextensively in contact, with II) an upper surface of aspunbond-meltblown-spunbond nonwoven synthetic carrier having 2 a basisweight of from about 9 gsm to about 30 gsm, which has a lower surfaceintegral with III) a first vapor-transmissive moisture barrier, whereinthe moisture barrier is hydrophobic or hydrophilic; wherein theabsorbent core has an air permeability of from about 3 to about 7m^(3/)min/m² (11-22 ft³/min/ft²).
 18. The filter element of claim 17,wherein the core further comprises in contact, optionally, coextensivelyin contact, with the upper surface of the first fibrous absorbent layerIV) a second fibrous absorbent layer comprising a) natural fibers,synthetic fibers or a mixture thereof, and b) a binder which is asynthetic binder fiber or powder, a hydrophilic emulsion polymer binderor a mixture thereof.
 19. The filter element of claim 17, wherein thecore has an absorbent capacity of from about 10 grams/gram to about 15grams/gram.
 20. The filter element of claim 17, wherein the corecontains superabsorbent material and the core has an absorbent capacityof from about 20 grams/gram to about 110 grams/gram.
 21. The unitaryabsorbent core of claim 17, wherein the core contains superabsorbentmaterial and the core has an absorbent capacity of from about 20grams/gram to about 50 grams/gram.